\makeatletter
\@ifundefined{HCode}
{\documentclass[screen, CRCHIM, Unicode, Thematic, published]{cedram}
\newenvironment{noXML}{}{}
\def\tsup#1{$^{{#1}}$}
\def\tsub#1{$_{{#1}}$}
\def\ndash{\text{--}}
\usepackage[T1]{fontenc}
\def\thead{\noalign{\relax}\hline}
\def\tbody{\noalign{\relax}\hline}
\def\endthead{\noalign{\relax}\hline}
\def\xsection#1{}
\def\tabnote#1{\vskip4pt\parbox{.83\linewidth}{#1}}
\RequirePackage{etoolbox}
\def\jobid{crchim20230919}
%\graphicspath{{/tmp/\jobid_figs/web/}}
\graphicspath{{./figures/}}
\newcounter{runlevel}
\let\MakeYrStrItalic\relax
\csdef{Seqnsplit}{\\}
\def\refinput#1{}
\def\back#1{}
\let\ubreak\newline
\def\botline{\\\hline}
\def\xxbotline{\hline}
\def\mn{\phantom{$-$}}
\def\0{\phantom{0}}
\def\inlinefig#1{\begin{center}\includegraphics{#1}\end{center}}
\usepackage{multirow} 
\def\nrow#1{\@tempcnta #1\relax%
\advance\@tempcnta by 1\relax%
\xdef\lenrow{\the\@tempcnta}}
\def\morerows#1#2{\nrow{#1}\multirow{\lenrow}{*}{#2}}
\def\xmorerows#1#2{#2}
\usepackage{hyperref}
\makeatletter
\g@addto@macro{\UrlBreaks}{\UrlOrds}
\gappto{\UrlBreaks}{\UrlOrds}
\makeatother
\DOI{10.5802/crchim.307}
\datereceived{2023-10-14}
\daterevised{2024-01-11}
\dateaccepted{2024-03-15}
\ItHasTeXPublished
}
{\documentclass[crchim]{article}
\usepackage[T1]{fontenc}
\def\CDRdoi{10.5802/crchim.307}
\let\newline\break
\def\xmorerows#1#2{\morerows{#1}{#2}}
\let\ubreak\relax
\makeatletter
\def\xxbotline{\botline}
\def\CDRsupplementaryTwotypes#1#2{}
}
\makeatother

\usepackage{upgreek}

\dateposted{2024-06-27}
\begin{document}

\begin{noXML}

%\makeatletter
%\def\TITREspecial{\relax}
%\def\cdr@specialtitle@english{French/Nordic Special Issue on Materials and Coordination Chemistry}
%\def\cdr@specialtitle@french{Num\'ero sp\'ecial franco-nordique sur les mat\'eriaux et la chimie de coordination}
%\makeatother

\CDRsetmeta{articletype}{research-article}

\title{(Pyridin-2-ylmethyl)porphyrins: synthesis, characterization and
C--N oxidative fusion attempts}

\alttitle{(Pyridin-2-ylmethyl)porphyrines : Synth\`{e}se,
caract\'{e}risation et essais de fusion C--N oxydante}

\author{\firstname{Mathieu} \lastname{Berthelot}\CDRorcid{0009-0005-0205-9465}}
\address{Institut de Chimie Mol\'{e}culaire de l'Universit\'{e} de
Bourgogne, UMR CNRS 6302, Universit\'{e} de Bourgogne, Facult\'{e} des
Sciences Mirande, Aile B-Chimie, 9 avenue Alain Savary - BP 47870,
21078 DIJON Cedex, France}
%\email{mathieu.berthelot@parisdescartes.fr}

\author{\firstname{Julie} \lastname{Echaubard}}
\addressSameAs{1}{Institut de Chimie Mol\'{e}culaire de
l'Universit\'{e} de Bourgogne, UMR CNRS 6302, Universit\'{e} de
Bourgogne, Facult\'{e} des Sciences Mirande, Aile B-Chimie, 9 avenue
Alain Savary - BP 47870, 21078 DIJON Cedex, France}
%\email{julie.echaubard@u-bourgogne.fr}

\author{\firstname{Asmae} \lastname{Bousfiha}}
\addressSameAs{1}{Institut de Chimie Mol\'{e}culaire de
l'Universit\'{e} de Bourgogne, UMR CNRS 6302, Universit\'{e} de
Bourgogne, Facult\'{e} des Sciences Mirande, Aile B-Chimie, 9 avenue
Alain Savary - BP 47870, 21078 DIJON Cedex, France}
%\email{asmae.bousfiha@u-bourgogne.fr}

\author{\firstname{Charles H.} \lastname{Devillers}\CDRorcid{0000-0001-9078-7035}\IsCorresp}
\addressSameAs{1}{Institut de Chimie Mol\'{e}culaire de
l'Universit\'{e} de Bourgogne, UMR CNRS 6302, Universit\'{e} de
Bourgogne, Facult\'{e} des Sciences Mirande, Aile B-Chimie, 9 avenue
Alain Savary - BP 47870, 21078 DIJON Cedex, France}
\email[C. H. Devillers]{charles.devillers@u-bourgogne.fr}

\shortrunauthors

\keywords{\kwd{Pyridinylporphyrin}\kwd{Pyridine}\kwd{Oxidative C--N
fusion}\kwd{\tralicstex{π}{$\uppi$}-extension}\kwd{Cyclic voltammetry}\kwd{NMR
spectroscopy}}

\altkeywords{\kwd{Pyridinylporphyrine}\kwd{Pyridine}\kwd{Fusion
oxydante C--N}\kwd{Voltamm\'{e}trie cyclique}\kwd{Spectroscopie RMN}}

\thanks{Universit\'{e} de Bourgogne, Universit\'{e} de Bourgogne
Franche-Comt\'{e}, CNRS (Centre National de la Recherche Scientifique),
Conseil R\'{e}gional de Bourgogne, Fonds Europ\'{e}en de
D\'{e}veloppement R\'{e}gional (FEDER), Agence Nationale de la Recherche
(ANR-15-CE28-0018-01), Conseil R\'egional de Bourgogne Franche-Comt\'e
and French ``Investissement d'Avenir'' program (ANR-15-IDEX-03)}

\begin{abstract}
A new route for the synthesis of
\textit{meso}-(pyridin-2-ylmethyl)porphyrins was developed, based on
the nucleophilic attack of (pyridin-2-ylmethyl)lithium reagent on a
porphyrin bearing one free \textit{meso} position. The latter is then
metalated with Zn(II) and Ni(II). These products were characterized by
NMR spectroscopy, UV--visible absorption spectroscopy, mass
spectrometry and electrochemistry. Attempts to generate the C--N-fused
compound by oxidation (new bond between the nitrogen of the pyridinyl
substituent and the \tralicstex{β}{$\upbeta$}-pyrrolic position of the porphyrin) are
also described.
\end{abstract}

\begin{altabstract}
Une nouvelle voie de synth\`{e}se de
\textit{meso}-(pyridin-2-ylm\'{e}thyl)porphyrine a \'{e}t\'{e}
d\'{e}velopp\'{e}e, bas\'{e}e sur l'attaque nucl\'{e}ophile du
r\'{e}actif (pyridin-2-ylm\'{e}thyl)lithium sur une porphyrine
poss\'{e}dant une position \textit{meso} libre. Cette derni\`{e}re est
ensuite m\'{e}tall\'{e}e par le Zn(II) et le Ni(II). Ces produits ont
\'{e}t\'{e} caract\'{e}ris\'{e}s par spectroscopie RMN, spectroscopie
d'absorption UV--visible, spectrom\'{e}trie de masse et
\'{e}lectrochimie. Nos essais concernant la r\'{e}action de fusion C--N
oxydante (nouvelle liaison entre l'azote du substituant pyridinyle et
la position \tralicstex{β}{$\upbeta$}-pyrrolique de la porphyrine) sont \'{e}galement
d\'{e}crits.
\end{altabstract}

\maketitle
{\vspace*{.9pc}}

\twocolumngrid

\end{noXML}

\section{Introduction} \label{sec1}

\looseness=-1
Pyridinyl-based porphyrins are quite rare in the literature since their
synthesis is cumbersome. Possible applications for these derivatives
have already been reported such as photo-electrochemistry~\cite{1},
light-harvesting charge separation systems~\cite{2,3}, supramolecular
chemistry~\cite{4,5,6,7,8,9,10,11,12,13}, catalysis~\cite{9,14}, fast
energy transfer~\cite{12,15}, molecular assembly on Au(III)~\cite{16}
and dendrimer formation~\cite{17}. The full development of these
pyridinylporphyrin derivatives may be restricted due to these synthetic
limitations. The main issue stems from the first condensation steps
with pyridinyl-based aldehyde and pyrrole, pyridinyl-based
dipyrromethane with aldehydes or dipyrromethane with pyridinyl-based
aldehydes, which results in low yields. Indeed, the pyridinyl fragment
is able to trap protons from the Br{\o}nsted acid catalyst or
deactivate the Lewis Acid catalyst in the common Adler and Longo or
Lindsey condensation reactions. In our group, we have been interested
in the exploitation of these pyridinyl-based porphyrins for molecular
recognition of phenol derivatives~\cite{18} but also as precursors of
C--N-fused cationic compounds obtained by oxidative
pathway~\cite{19,20}. For this latter purpose,
mercaptopyridinylporphyrins have been successfully fused and the
original physicochemical properties of the C--N-fused porphyrins have
been explored in details ({Previous work}, Scheme~\ref{sch1}).
To extend the scope of this C--N oxidative fusion reaction, we wanted
to replace the sulfur atom by a carbon atom and investigate if this
reaction could work ({This work}, Scheme~\ref{sch1}).

\begin{scheme*}[t!]
{\vspace*{-.2pc}}
\includegraphics{sc01}
{\vspace*{.5pc}}
\caption{\label{sch1}Previous work: C--N oxidative fusion with a
mercaptopyridinylporphyrin; This work: planned target obtained after
C--N oxidative fusion of a pyridinylmethylporphyrin precursor.}
{\vspace*{-.5pc}}
\end{scheme*}

This manuscript describes the synthesis and characterization of
(pyridin-2-ylmethyl)porphyrin $\mathbf{H}_{\mathbf{2}}$\textbf{-7}
(Scheme~\ref{sch3}) as well as the synthesis of its respective Zn(II)
and Ni(II) complexes \textbf{Zn-7} and \textbf{Ni-7}. Preliminary C--N
oxidative fusion attempts are also \mbox{described}.

\section{Results and discussion} \label{sec2}
\subsection{Synthesis of (pyridin-2-ylmethyl)porphyrins $\mathbf{2}$,
$\mathbf{Zn}$\textbf{-}$\mathbf{2}$
and\,\,$\mathbf{Ni}$\textbf{-}$\mathbf{2}$} \label{sec2.1}

\looseness=-1
Our initial objective was to synthesize
5,10,15,20-tetrakis(pyridin-2-ylmethyl)porphyrin
$\mathbf{H}_{\mathbf{2}}$\textbf{-1} by condensation of pyrrole with
aldehyde \textbf{2} produced by oxidation of commercially available
2-(2-hydroxyethyl)pyridine (\textbf{3}, Scheme~\ref{sch2}).

\begin{scheme*}[t!]
\includegraphics{sc02}
{\vspace*{.4pc}}
\caption{\label{sch2}Attempted synthesis of
5,10,15,20-tetrakis(pyridin-2-ylmethyl)porphyrin
$\mathbf{H}_{\mathbf{2}}$\textbf{-1}.}
{\vspace*{-.5pc}}
\end{scheme*}

Two experimental conditions were tested for the aldehyde \textbf{2}
synthesis: Swern conditions, using oxalyl chloride in DMSO and
oxidation by a cerium(IV)-based oxidant~\cite{21,22}. Despite several
attempts with these two oxidants, the oxidation step of the alcohol
function systematically failed. The targeted aldehyde \textbf{2} may be
in equilibrium with its enol form~\cite{23}, which could explain the
difficulties in isolating/forming this aldehyde. Given these
disappointing results, an alternative route was developed. The latter
was based on the synthesis of a porphyrin monofunctionalized at the
\textit{meso} position with 2-methylpyridine (Scheme~\ref{sch3}). 

\begin{scheme*}[t!]
\includegraphics{sc03}
{\vspace*{.6pc}}
\caption{\label{sch3}Synthesis of (pyridin-2-ylmethyl)porphyrin
$\mathbf{H}_{\mathbf{2}}$\textbf{-7} and the corresponding Zn(II) and
Ni(II) complexes \textbf{Zn-7} and \textbf{Ni-7}.}
{\vspace*{-.5pc}}
\end{scheme*}

The first step consisted in the preparation of the
(pyridin-2-ylmethyl)lithium (\textbf{5}) reagent by addition of
\textit{n}-butyllithium on 2-picoline (\textbf{6}). This orange
solution was then added in excess to the
tri-\textit{meso}-arylporphyrin $\mathbf{H}_{\mathbf{2}}$\textbf{-4}
following a protocol similar to the one previously described by Senge
and colleagues for the phenylation of porphyrins~\cite{24}. Under these
conditions, the original (pyridin-2-ylmethyl)porphyrin
$\mathbf{H}_{\mathbf{2}}$\textbf{-7} was isolated in 63\% yield
(Scheme~\ref{sch3}). The corresponding Zn(II) and Ni(II) complexes
(\textbf{Zn-7} and \textbf{Ni-7}, respectively) were also synthesized
in good yields by standard metalation procedure (see experimental part)
using the respective acetate salts~\cite{25}. It should be noted that
another report from Barbe and coworkers describes the synthesis of a
pyridin-2-ylmethylporphyrin (\textbf{Zn-14},
Scheme~\ref{sch4})~\cite{26}. This synthesis was based on the Suzuki
cross-coupling of 5-bromo-2-chloromethyl-pyridine (\textbf{13})
(synthesized in two steps from bromopicolinaldehyde (\textbf{11}),
Scheme~\ref{sch4}) with zinc(II) \textit{meso}-substituted
dioxoborolaneporphyrin \mbox{\textbf{Zn-10}} (synthesized in three
steps from the 5,10,15-trimesitylporphyrin). According to these authors
and contrary to their expectations, only the chlorinated carbon atom of
\textbf{13} was coupled with the porphyrin and not the brominated one.

\begin{scheme*}[t!]
{\vspace*{-.1pc}}
\includegraphics{sc04}
{\vspace*{.6pc}}
\caption{\label{sch4}Synthesis of pyridin-2-ylporphyrin \textbf{Zn-14}
as described by Barbe and coworkers~\cite{26}.}
{\vspace*{-1pc}}
\end{scheme*}

Thus our proposed synthesis is more straightforward since it involves
only two steps for the synthesis of
$\mathbf{H}_{\mathbf{2}}$\textbf{-7} starting from the
tri-\textit{meso}-arylporphyrin $\mathbf{H}_{\mathbf{2}}$\textbf{-4}.

\subsection{Characterization of
(pyridin-2-{\ubreak}ylmethyl)porphyrins
$\mathbf{H}_{\mathbf{2}}$\textbf{-}$\mathbf{7}$,
$\mathbf{Zn}$\textbf{-}$\mathbf{7}$
and\,\,$\mathbf{Ni}$\textbf{-}$\mathbf{7}$} \label{sec2.2}

\subsubsection{NMR characterization of
(pyridin-2-{\ubreak}ylmethyl)porphyrins
$\mathbf{H}_{\mathbf{2}}$\textbf{-}$\mathbf{7}$,
$\mathbf{Zn}$\textbf{-}$\mathbf{7}$
and\,\,$\mathbf{Ni}$\textbf{-}$\mathbf{7}$} \label{sec2.2.1}

A focus on the aromatic part of the ${}^{1}\text{H}$ NMR spectra of
compounds \textbf{6}, $\mathbf{H}_{\mathbf{2}}$\textbf{-7},
\textbf{Zn-7} and \textbf{Ni-7} is presented in Figure~\ref{fig1}.
Noteworthy, for \textbf{Zn-7}, CDCl$_3$ had to be replaced by
(CD$_3$)$_2$CO due to solubility problems. In addition, one drop of
pyridine-$d_{\mathit{5}}$ was used to prevent the formation of
coordination polymers upon coordination of the pyridinyl nitrogen atom
onto the metallic center of another \textbf{Zn-7} porphyrin. 2-Picoline
\textbf{6} is characterized by a singlet at 2.33~ppm for the methyl
group and four multiplets between 6.84~ppm and 8.28~ppm. The
${}^{1}\text{H}$ NMR spectra of $\mathbf{H}_{\mathbf{2}}$\textbf{-7},
\textbf{Zn-7} and \textbf{Ni-7} show similar chemical shifts for the
pyridinyl moiety ($6.73 < \delta < 7.32$~ppm) except for the $\alpha$
proton doublet which appears between 8.59 and 8.75~ppm. For comparison
purpose, the $\alpha$ proton doublet of \textbf{6} appears at a
slightly lower chemical shift (8.28~ppm). Thus the porphyrin ring has
little influence on the chemical shifts of the pyridinyl moiety
contrary to what is observed for the --CH$_2$-- spacer for which the
methylene singlets of $\mathbf{H}_{\mathbf{2}}$\textbf{-7},
\mbox{\textbf{Zn-7}} and \textbf{Ni-7} are observed between 6.21 and
6.70~ppm, a much higher value as compared to 2.33~ppm for~\textbf{6}.
The same range of chemical shift was observed by Barbe and coworkers
with the free-base analogue of \textbf{Zn-14}~\cite{26}, where the
methylene bridge appeared at 6.59~ppm. This behavior is typically
observed for protons that are lying outside the shielding cone of the
porphyrin. The \mbox{$\upbeta$-pyrrolic} protons of
$\mathbf{H}_{\mathbf{2}}$\textbf{-7}, \mbox{\textbf{Zn-7}} and
\textbf{Ni-7} are located between 8.70 and~9.74~ppm. The~more
deshielded \mbox{$\upbeta$-pyrrolic} doublet appears between 9.32 and
9.74~ppm and is attributed to the protons that are closest to the
methylpyridinyl \mbox{substituent}.

\begin{figure*}
\includegraphics{fig01}
\caption{\label{fig1}Partial ${}^{1}\text{H}$ NMR spectra of
\textbf{6}, $\mathbf{H}_{\mathbf{2}}$\textbf{-7}, \textbf{Zn-7} and
\textbf{Ni-7} (CDCl$_3$ ((CD$_3$)$_2$CO $+$ one drop of
pyridine-$d_{\mathit{5}}$ for \textbf{Zn-7}), 500~MHz, 298~K). The
asterisk $*$ indicates not fully deuterated pyridine signals in the
$^{1}$NMR spectrum of \textbf{Zn-7}. Small signals observed on the
$^{1}$NMR spectrum of \textbf{6} correspond to unknown impurities that
are present in the commercial reagent.}
{\vspace*{-.25pc}}
\end{figure*}

\subsubsection{UV--visible absorption spectroscopy of
$\mathbf{H}_{\mathbf{2}}$\textbf{-}$\mathbf{7}$,
$\mathbf{Zn}$\textbf{-}$\mathbf{7}$
and\,\,$\mathbf{Ni}$\textbf{-}$\mathbf{7}$} \label{sec2.2.2}

UV--visible absorption spectra of $\mathbf{H}_{\mathbf{2}}$\textbf{-7},
\textbf{Zn-7} and \textbf{Ni-7} are presented in Figure~\ref{fig2}.
Porphyrin $\mathbf{H}_{\mathbf{2}}$\textbf{-7} exhibits a Soret band at
419~nm and four less intense Q~bands at 516, 552, 592 and 648~nm, as
expected for a free base porphyrin. The corresponding nickel(II)
complex \textbf{Ni-7} shows a 3-nm hypsochromic shift of the Soret band
as compared to $\mathbf{H}_{\mathbf{2}}$\textbf{-7}. Indeed, while the
metallic cation accepts the lone-pair electrons of the nitrogen atoms
of the porphyrin ring, its electrons are donated to the macrocycle. The
resulting flow of electrons of the delocalized $\uppi$-system increases
the energy available for electron transition, leading to the blueshift
observed for the Soret band of \textbf{Ni-7}~\cite{27}. The number of
Q~bands for this derivative is reduced to one as shown by comparison
with the UV--visible absorption spectrum of
$\mathbf{H}_{\mathbf{2}}$\textbf{-7},{\break} in~agreement with the
enhanced symmetry of the porphyrin induced by the metalation.

\begin{figure}
\includegraphics{fig02}
{\vspace*{-.3pc}}
\caption{\label{fig2}UV--visible absorption spectra of
\mbox{$\mathbf{H}_{\mathbf{2}}$\textbf{-7}} (black curve),
\textbf{Zn-7} (red-curve) and \textbf{Ni-7} (blue curve) in
CH$_2$Cl$_2$ or for \textbf{Zn-7} in DMF.}
\end{figure}

In the specific case of \textbf{Zn-7}, the CH$_2$Cl$_2$ solvent had to
be replaced by DMF to improve the solubility of the porphyrin by
preventing the formation of the coordination polymers. The Soret band
is observed at 427~nm and only two Q~bands are seen at 561 and 601~nm,
for symmetry reasons.

\subsubsection{Electrochemical characterization
of\,\,$\mathbf{H}_{\mathbf{2}}$\textbf{-}$\mathbf{7}$,
$\mathbf{Zn}$\textbf{-}$\mathbf{7}$
and\,\,$\mathbf{Ni}$\textbf{-}$\mathbf{7}$} \label{sec2.2.3}

All potential values reported in this manuscript are {vs.}\ the
saturated KCl calomel electrode (SCE), unless otherwise mentioned. The
cyclic voltammogram of \textbf{Ni-7} is presented in Figure~\ref{fig3}
(top black curve). The first fully irreversible oxidation takes place
at $E_{\mathrm{pa}}(\text{O}1) = 0.85$~V which is less positive than
the first oxidation potentials of Ni(II) porphyrins functionalized with
2-mercaptopyridine ($E_{\mathrm{pa}} \approx 1.10$~V) \cite{19}. This
behavior agrees with the donor inductive effect of the --CH$_2$--
group, compared to the sulfur atom involved in a thioether function.
This irreversibility which follows the porphyrin cation radical
formation might also be a good indication that the \mbox{C--N} fusion
reaction takes place. Two other reversible \mbox{oxidation} peaks are
observed at $E_{\mathrm{pa}}(\text{O}2) = 0.98$~V and{\break}
$E_{\mathrm{pa}}(\text{O}3) = 1.29$~V. Only one poorly reversible
reduction peak is seen at $E_{\mathrm{pc}}(\text{R}1) = -1.56$~V.

\begin{figure}
\includegraphics{fig03}
{\vspace*{-.3pc}}
\caption{\label{fig3}Cyclic voltammograms of \textbf{Ni-7} (top, black
curve) and \textbf{Zn-7} (bottom, blue curve). Conditions: $C =
10^{-3}$~M, CH$_2$Cl$_2$ 0.1~M TBAPF$_6$, WE $=$ Pt {\O} $=$ 2~mm, $v =
100~\text{mV}{\cdot}\text{s}^{-1}$. For solubility reason, 1.0 equiv of
pyridine has been added to the solution containing \textbf{Zn-7}.}
{\vspace*{-.4pc}}
\end{figure}

The zinc(II) complex \textbf{Zn-7} exhibits very low solubility in
CH$_2$Cl$_2$. The latter probably arises from coordination polymers
that may be formed by coordination of the pyridinyl moiety onto the
zinc(II) atom of another porphyrin~\cite{3,10,11,17}. This behavior has
been already experienced by us with the zinc(II) \mbox{complexes}
substituted by one or two \mbox{mercaptopyridinyl}
fragment(s)~\cite{20}. The addition of 1.0 equiv of pyridine to a
solution of \textbf{Zn-7} in CH$_2$Cl$_2$ was supposed to break the
coordination polymers. Indeed, all the porphyrin became soluble which
supported our initial hypothesis. The first oxidation wave is much more
reversible than for \textbf{Ni-7} ($E_{\mathrm{pa}}(\text{O}1') =
0.57$~V, $E_{1/2} = 0.53$~V, $\Delta E_p = 80$~mV). Two other
irreversible oxidation peaks are observed at ca.
$E_{\mathrm{pa}}(\text{O}2') = 1.05$~V and
($E_{\mathrm{pa}}(\text{O}3') = 1.27$~V. The \mbox{reduction} peak
$\text{R}1'$ is almost reversible and is observed at
$E_{\mathrm{pc}}(\text{R}1') = -1.66$~V.

\subsection{Oxidative C--N fusion attempts} \label{sec2.3}

Following our previous work on the oxidative \mbox{C--N} fusion of
pyri(mi)dine-based porphyrins (see Scheme~\ref{sch1} and
Refs.~\cite{19,20,28}), fusion tests have been performed in
CH$_2$Cl$_2$ on \textbf{Ni-7} and \textbf{Zn-7} with PIFA
((bis(trifluoroacetoxy)iodo)benzene), a two-electron acceptor. In
principle, if the C--N oxidative fusion reaction of 2-picoline on the
porphyrin nucleus occurs, the use of a base to neutralize the protons
released by the C--N coupling reaction is necessary. Indeed, unlike
2-mercaptopyridine whose $\text{p}K_a$ is very low
(${-}$1.07)~\cite{29,30}, 2-picoline has a $\text{p}K_a$ of
5.96~\cite{31} which is higher than that of trifluoroacetate ions
($\text{p}K_a = 0.23$). Thus, the trifluoroacetate anions released
during the reduction of PIFA are no longer sufficiently basic to
capture the protons released during the formation of the C--N bond. A
first reaction test between \textbf{Ni-7} and PIFA was carried out in
CH$_2$Cl$_2$ in the presence of potassium carbonate as a base. After
reacting for 1~h with 1.0 equiv of PIFA, a brown product, more polar
than compound \textbf{Ni-7}, was observed on a TLC plate (SiO$_2$,
CH$_2$Cl$_2$). Then 0.2 and 0.8 equiv of PIFA were added at one-hour
intervals. One hour after the last addition of oxidant, the stirring
was stopped because no further development was observed. 2,6-Lutidine,
whose $\text{p}K_a$ is 6.72~\cite{31}, is perfectly miscible under our
experimental conditions, unlike potassium carbonate which mainly
remains as a precipitate. This organic base was therefore chosen for a
new C--N fusion test of 2-picoline on the porphyrin core. Thus, the
reaction between \textbf{Ni-7} and PIFA, in the presence of 2.0 equiv
of 2,6-lutidine, in dichloromethane, was monitored by TLC (SiO$_2$,
CH$_2$Cl$_2$), in order to determine the amount of oxidant necessary
for the consumption of the starting product. After 23~h of reaction at
room temperature and addition of 2.0 equiv of PIFA, the crude reaction
no longer seemed to evolve. The latter contained \textbf{Ni-7} and a
more polar brown product which did not migrate onto the TLC plate.
MALDI-TOF mass spectrometry analysis of the crude reaction shows a peak
at $m/z = 712.1$, attributed to the C--N fusion product ($m/z =
712.2026$), a peak at $m/z = 713.1$ corresponding to \textbf{Ni-7} and
a more intense peak at $m/z = 726.1$ corresponding to the exact mass of
compound \textbf{Ni-7} to which 13 mass units are added. This mass may
be related to the fusion of 2-picoline with porphyrin and formation of
a carbonyl on the CH$_2$ bridge (Figure~\ref{fig4}).

\begin{figure*}
\includegraphics{fig04}
\caption{\label{fig4}MALDI-TOF spectrum (global and zoom views)
obtained from the crude solution resulting from the addition of 2.0
equiv of 2,6-dimethylpyridine and 2.0 equiv of PIFA on \textbf{Ni-7},
after stirring for 23~h in CH$_2$Cl$_2$.}
\end{figure*}

Two chemical fusion tests were also carried out on \textbf{Zn-7} with
PIFA at room temperature in dichloromethane, one in the presence of 2.0
equiv of potassium carbonate, the other in the presence of 2.0 equiv of
2,6-lutidine. When the reaction is carried out in the presence of
potassium carbonate as base, 1.8 equiv (first 1.0 equiv, then 1.5~h of
stirring, then 0.8 additional equiv added in 4 times at one-hour
intervals) of PIFA are necessary to consume all the precursor. Under
these conditions, two products are formed, one being more polar
(purple/pink) and the other less polar (dark purple) than the product
\textbf{Zn-7} (purple). The ${}^{1}\text{H}$ NMR analysis of the raw
reaction product carried out in acetone-$d_6$ in the presence of a drop
of pyridine-$d_5$ did not give any information (poorly resolved
signals). An ESI mass analysis was performed to obtain more
information, but none of the observed peaks could be assigned. The
oxidation of compound \textbf{Zn-7} in the presence of 2,6-lutidine
only leads to the formation of a single dark purple product, more polar
than the precursor to be fused. In this case, the use of a total of 2.2
equiv of PIFA did not allow all the starting material to be consumed,
even after 23~h of reaction. MALDI-TOF analysis of the crude reaction
(Figure~\ref{fig5})
shows a peak at an $m/z$ value of 719.1 corresponding to the initial
product ($m/z$ theoretical $=$ 719.2027) but also at $m/z = 718.1$
(C--N coupling product, theoretical $m/z = 718.1944$) and 717.1 (loss
of an additional proton), all three minor in terms of intensity
compared to a peak at 732.1, whose $m/z$ ratio corresponds to the mass
of \textbf{Zn-7} to which 13 units of mass are added. The latter may,
as in the case of the oxidation of derivative \textbf{Ni-7}, correspond
to the fusion product with the formation of a carbonyl function on the
bridging carbon atom. Finally, an isotopic cluster between $m/z = 1435$
and $m/z = 1445$ is also observed. It could be assigned to the
formation of a dimer of unknown structure.

\begin{figure*}
{\vspace*{-1pt}}
\includegraphics{fig05}
{\vspace*{-2pt}}
\caption{\label{fig5}MALDI-TOF spectrum (global and zoom views)
obtained from the crude solution resulting from the addition of 2.0
equiv of 2,6-dimethylpyridine and 2.0 equiv of PIFA on \textbf{Zn-7},
after stirring for 23~h in CH$_2$Cl$_2$.}
{\vspace*{-.3pc}}
\end{figure*}

\section{Experimental section} \label{sec3}

{\vspace*{-2pt}}

\subsection{Reagents and instrumentation} \label{sec3.1}

Unless otherwise noted, all reactions were carried out without
protection from air.\ CH$_2$Cl$_2$, MeCN, THF were dried over alumina
cartridges using a solvent purification system PureSolv PS-MD-5 model
from Innovative Technology and kept under argon. The following reagents
were used: \mbox{$n$-BuLi} (1.6~M in hexane, Acros Organics),
2-picoline (98\%, Acros Organics),
2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ, 98\%, Sigma-Aldrich),
[bis(trifluoroacetoxy)iodo]benzene ((PIFA), 98\%, Acros Organics),
2,6-lutidine (99\%, Sigma-Aldrich), pyridine (99\%, Acros Organics),
K$_2$CO$_3$ (99\%, anhydrous, Alfa Aesar),
$\text{Zn(OAc)}_2{\cdot}2\text{H}_2\text{O}$ (99.5\%, Acros Organics),
$\text{Ni(OAc)}_2{\cdot}4\text{H}_2\text{O}$ (99\%, Alfa Aesar),
10-phenyl-5,15-di-p-tolylporphyrin $\mathbf{H}_{\mathbf{2}}$\textbf{-4}
was synthesized as reported in~\cite{32}. Our data (${}^{1}\text{H}$
NMR, ${}^{13}\text{C}$~NMR, \mbox{UV--Visible} absorption, and MALDI-TOF
mass spectrum) were consistent with those described in Ref.~\cite{32}.
Tetra-\textit{n}-butylammonium hexafluorophosphate was synthesized by
mixing stoichiometric amounts of HPF$_6$ (60\% in water, Acros
Organics) and tetra-\textit{n}-butylammonium hydroxide (40\% in water,
Alfa Aesar). The resulting solution was filtrated on a B\"{u}chner
filter under vacuum and the white crystals were collected. These
crystals were recrystallized twice in EtOH and then dried in a stove at
110~{\textdegree}C for 48~h.

${}^{1}\text{H}$, ${}^{13}\text{C}$ NMR spectra were recorded either on
a Bruker Avance 400, on a Bruker Avance 500 or on a Bruker Avance 600
III HD spectrometer. Chemical shifts are expressed in parts per million
(ppm) from the residual non-deuterated solvent signal~\cite{33}.
$J$~values are expressed in Hz.

High-resolution mass spectra (HRMS) were recorded either on a Thermo
LTQ Orbitrap XL \mbox{apparatus} equipped with an ESI source or on a
Bruker UltraflexII LRF 2000 MALDI-TOF mass spectrometer (matrix:
dithranol).

UV--visible absorption spectra were recorded on a VARIAN Cary 50
UV--Visible spectrophotometer using quartz cells.

All electrochemical manipulations were performed using Schlenk
techniques in an atmosphere of dry oxygen-free argon at room
temperature ($T = 20~\text{\textdegree C} \pm 3~\text{\textdegree
C}$). The supporting electrolyte was degassed under vacuum before use
and then dissolved to a concentration of
$0.1~\text{mol}{\cdot}\text{L}^{-1}$. Voltammetric analyses were
carried out in a standard three-electrode cell, with an Autolab PGSTAT
302~N potentiostat, connected to an interfaced computer that employed
Electrochemistry Nova software or on a Biologic SP-300 potentiostat,
connected to an interfaced computer that employed EC-Lab (v.~11.25)
software. The reference electrode was a saturated KCl calomel electrode
(SCE) separated from the analysed solution by a sintered glass disk
filled with the background solution. The auxiliary electrode was a
platinum wire separated from the analysed solution by a sintered glass
disk filled with the background solution. For all voltammetric
measurements, the working electrode was a platinum disk electrode
(\textit{{\O}}~$=$ 1.6~mm). In these conditions, when operating in
CH$_2$Cl$_2$ (0.1~M TBAPF$_6$), the formal potential for the ferrocene
(${+}/0$) couple was ${+}$0.46~V.
\vspace*{-.65pc}

\subsection{Synthesis of
5-(Pyridin-2-methyl)-10,20-{\ubreak}bis(p-tolyl)-15-phenylporphyrin
($\mathbf{H}_{\mathbf{2}}$\textbf{-}$\mathbf{7}$)}
\vspace*{-.15pc}

\inlinefig{fx01}

This protocol was inspired by the one described by Senge and coworkers
for aryl and alkyl functionalization of porphyrins~\cite{24}. A 20~mL
Schlenk flask was evacuated and flushed with argon three times.
2-Picoline ($197.5~\upmu$L, 2.0~mmol, 1.0 equiv) was then added to the
Schlenk flask followed by dry THF (0.88~mL). The solution was cooled to
${-}$10~{\textdegree}C then a commercial solution of $n$-BuLi (1.6~M in
$n$-hexane) was added dropwise (1.25~mL, 2.0~mmol, 1.0~equiv). The
resulting orange solution was stirred at room temperature for 1~h.
$\mathbf{H}_{\mathbf{2}}$\textbf{-4} (100.00~mg, $1.76 \times
10^{-1}$~mmol, 1.0~equiv) was kept under vacuum for 2~h in a second
Schlenk flask and then flushed with argon. Dry THF (45~mL) was then
introduced into the Schlenk flask containing the porphyrin and the
solution was cooled to ${-}$30~{\textdegree}C. 1.2~mL (1.032~mmol, 6.0
equiv) of the orange solution obtained in the first Schlenk flask were
added dropwise to the solution of porphyrin. The resulting solution was
stirred at room temperature for 20~min, then a solution of H$_2$O
(0.84~mL) and dry THF (8.4~mL) previously degassed by bubbling argon
was added dropwise to the reaction mixture. The green solution was
stirred for a further 10~min at room temperature and DDQ (163.72~mg,
$7.07 \times 10^{-1}$~mmol, 4.0 equiv) was added to the Schlenk flask.
The resulting red solution was stirred at room temperature for 1~h and
then filtered on a pad of alumina, eluting with CH$_2$Cl$_2$. The crude
product was purified by column chromatography (SiO$_2$,
CH$_2$Cl$_2$/CH$_3$OH (99.5:0.5, v/v)). Three fractions were collected
containing an unknown impurity (Fraction~1),
$\mathbf{H}_{\mathbf{2}}$\textbf{-7} (Fraction~2) and traces of a
product which could be unreacted $\mathbf{H}_{\mathbf{2}}$\textbf{-4}
(Fraction~3). Fraction~2 was recrystallized in a CH$_2$Cl$_2$/CH$_3$OH
mixture. The obtained precipitate was filtered under vacuum, washed
with CH$_3$OH and dried at 110~{\textdegree}C overnight to give
$\mathbf{H}_{\mathbf{2}}$\textbf{-7} in 63\% yield (74.28~mg, $1.13
\times 10^{-1}$~mmol). ${}^{1}\text{H}$ NMR (CDCl$_3$, 500~MHz, 298~K):
$\delta$ (ppm) 9.52 (d, ${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 4.8$~Hz,
2H), 8.94 (d, ${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 4.8$~Hz, 2H), 8.85 (d,
${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 4.8$~Hz, 2H), 8.82 (d,
${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 4.7$~Hz, 2H), 8.75 (ddd,
${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 5.0$~Hz, ${}^4J_{\mathrm{H}\ndash
\mathrm{H}} = 1.9$~Hz, ${}^4J_{\mathrm{H}\ndash\mathrm{H}} = 0.9$~Hz, 1H),
8.21, (dd, ${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 7.7$~Hz,
${}^4J_{\mathrm{H}\ndash\mathrm{H}} = 1.6$~Hz, 2H), 8.09 (d,
${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 7.9$~Hz, 4H), 7.82 $-$ 7.70 (m, 3H),
7.55 (d, ${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 7.6$~Hz, 4H), 7.21 (td,
${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 7.7$~Hz, ${}^4J_{\mathrm{H}\ndash
\mathrm{H}} = 1.9$~Hz, 1H), 7.04 (ddd, ${}^3J_{\mathrm{H}\ndash\mathrm{H}}
= 7.3$~Hz, ${}^4J_{\mathrm{H}\ndash\mathrm{H}} = 5.0$~Hz,
${}^4J_{\mathrm{H}\ndash\mathrm{H}} = 1.2$~Hz, 1H), 6.75 (d,
${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 8.1$~Hz, 1H), 6.65 (s, 2H), 2.72 (s,
6H), $-$2.64 (s, 2H); ${}^{13}\text{C}\{{}^1\text{H}\}$ NMR (CDCl$_3$,
126~MHz, 298~K): $\delta$ (ppm) 164.1, 149.1, 142.2, 139.4, 137.5,
136.6, 134.6, 134.6, 127.8, 127.5, 126.8, 124.5, 121.1, 120.2, 120.1,
114.7, 43.7, 21.7; $\text{R}_f$ 0.07 (SiO$_2$, CH$_2$Cl$_2$);
$\lambda_{\mathrm{max}}$ (CH$_2$Cl$_2$)/nm (log~$\varepsilon$): 419
(5.76), 516 (4.35), 552 (4.10), 592 (3.81), 648 (3.71); HRMS (ESI+):
$m/z$ cald for C$_{46}$H$_{35}$N$_5$ [M $+$ H]$^+$ 658.29652, found
658.29638.

\subsection{Synthesis of
[5-(Pyridin-2-methyl)-10,20-{\ubreak}bis(p-tolyl)-15-phenylporphyrinato]zinc(II){\hfill\break}
($\mathbf{Zn}$\textbf{-}$\mathbf{7}$)}

\inlinefig{fx02}
\bigskip

A solution of $\mathbf{H}_{\mathbf{2}}$\textbf{-7} (30.05~mg, $4.57
\times 10^{-2}$~mmol, 1.0 equiv) and
$\text{Zn(OAc)}_2{\cdot}2\text{H}_2\text{O}$ (10.20~mg, $9.16 \times
10^{-2}$~mmol, 2.0 equiv) in a mixture of CHCl$_3$ (2.7~mL) and
CH$_3$OH (1.0~mL) was stirred at 60~{\textdegree}C for 1.5~h,
monitoring the progress of the reaction by TLC (SiO$_2$, CH$_2$Cl$_2$).
The solvent was then removed by rotary evaporation and the crude
product was recrystallized in a CH$_2$Cl$_2$/CH$_3$OH mixture. The
precipitate was filtered under vacuum, washed with a small amount of
CH$_3$OH and dried at 110~{\textdegree}C overnight to give
\mbox{\textbf{Zn-7}} in 81\% yield (26.72~mg, $3.71 \times
10^{-2}$~mmol). ${}^1\text{H}$ NMR ((CD$_3$)$_2$CO $+$ one drop
pyridine-$d_{\mathit{5}}$, 500~MHz, 298~K): $\delta$ (ppm) 9.75 (d,
${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 4.7$~Hz, 2H), 8.92, (d, 
${}^3J_{\mathrm{H}\ndash
\mathrm{H}} = 4.7$~Hz, 2H), 8.84 (d, ${}^3J_{\mathrm{H}\ndash\mathrm{H}} =
4.6$~Hz, 2H), 8.81 (d, ${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 4.6$~Hz, 2H),
8.59 (ddd, ${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 5.0$~Hz,
${}^4J_{\mathrm{H}\ndash\mathrm{H}} = 1.9$~Hz, ${}^4J_{\mathrm{H}\ndash
\mathrm{H}} = 0.9$~Hz, 1H), 8.19 (dd, ${}^3J_{\mathrm{H}\ndash\mathrm{H}}
= 7.6$~Hz, ${}^4J_{\mathrm{H}\ndash\mathrm{H}} = 1.7$~Hz, 2H), 8.06 (d,
${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 7.8$~Hz, 4H), 7.80--7.70 (m, 3H),
7.57 (d, ${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 7.5$~Hz, 4H), 7.34--7.29
(m, 1H), 7.03 (ddd, ${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 7.3$~Hz,
${}^4J_{\mathrm{H}\ndash\mathrm{H}} = 4.9$~Hz, ${}^4J_{\mathrm{H}\ndash
\mathrm{H}} = 1.2$~Hz, 1H), 6.93 (d, ${}^3J_{\mathrm{H}\ndash\mathrm{H}} =
8.1$~Hz, 1H), 6.70 (s, 2H), 2.68 (s, 3H);
${}^{13}\text{C}\{{}^1\text{H}\}$ NMR ((CD$_3$)$_2$CO $+$ one drop
Pyridine-$d_{\mathit{5}}$, 126~MHz, 298~K): $\delta$ (ppm) 151.8,
150.9, 150.7, 150.4, 150.2, 150.0, 149.7, 141.4, 137.7, 137.7, 136.8,
136.8, 136.3, 136.1, 135.9, 135.2, 135.2, 133.0, 132.4, 132.2, 130.7,
128.1, 127.9, 127.3, 124.6, 124.2, 124.0, 123.8, 121.5, 121.2, 117.0,
21.5; $\text{R}_{f}$ 0.47 (SiO$_2$, CH$_2$Cl$_2$);
$\lambda_{\mathrm{max}}$ (DMF)/nm (log~$\varepsilon$): 406 (4.55), 427
(5.70), 561 (4.05), 600 (3.44); HRMS (ESI+): $m/z$ cald for
C$_{46}$H$_{33}$N$_5$Zn [M $+$ H]$^+$ 720.21002, found 720.21151.

\vspace*{3pt}

\subsection{Synthesis of
[5-(Pyridin-2-methyl)-{\ubreak}10,20-bis(p-tolyl)-15-{\ubreak}phenylporphyrinato]nickel(II)
($\mathbf{Ni}$\textbf{-}$\mathbf{7}$)}
\vspace*{.8pc}

\inlinefig{fx03}
\bigskip

A Schlenk flask containing $\mathbf{H}_{\mathbf{2}}$\textbf{-7}
(40.02~mg, $6.08 \times 10^{-2}$~mmol, 1.0 equiv) and $\text{Ni(OAc)}_2
{\cdot} 4\text{H}_2\text{O}$ (30.31~mg, $1.22 \times 10^{-1}$~mmol, 2.0
equiv) was evacuated and flushed with argon three times. Dry DMF (3~mL)
was then added and the solution was stirred at 160~{\textdegree}C under
argon for 1.5~h, monitoring the progress of the reaction by TLC
(SiO$_2$, CH$_2$Cl$_2$). The red solution obtained was allowed to cool
to room temperature, then water was added (10~mL) to precipitate the
product. The precipitate obtained was filtered under vacuum, washed
with water and dried at 150~{\textdegree}C under vacuum for 4.5~h to
give \textbf{Ni-7} in 84\% yield (36.61~mg, $5.12 \times
10^{-2}$~mmol). ${}^1\text{H}$ NMR (CDCl$_3$, 500~MHz, 298~K):
$\delta$ (ppm) 9.31 (d, ${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 5.0$~Hz,
2H), 8.81 (d, ${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 4.9$~Hz, 2H), 8.73 (d,
${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 4.9$~Hz, 2H), 8.69 (d,
${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 4.9$~Hz, 2H),
8.67 (d, ${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 5.0$~Hz, 1H), 7.99 (d,
${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 6.4$~Hz, 2H), 7.87 (d,
${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 7.5$~Hz, 4H), 7.74 $-$ 7.61 (m, 3H),
7.47 (d, ${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 7.6$~Hz, 4H), 7.24 (d,
${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 9.5$~Hz, 1H), 7.03 (t,
${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 6.2$~Hz, 1H), 6.73 (d,
${}^3J_{\mathrm{H}\ndash\mathrm{H}} = 8.1$~Hz, 1H), 6.21 (s, 2H), 2.64 (s,
2H); ${}^{13}\text{C}\{{}^1\text{H}\}$ NMR (CDCl$_3$, 126~MHz, 298~K):
$\delta$ (ppm) 149.1, 143.2, 142.7, 142.5, 141.0, 138.0, 137.6, 136.6,
133.8, 133.7, 133.2, 132.4, 132.2, 130.2, 127.8, 127.7, 127.0, 124.1,
121.1, 118.9, 113.3, 21.6; $\text{R}_f$ 0.17 (SiO$_2$, CH$_2$Cl$_2$);
$\lambda_{\mathrm{max}}$ (CH$_2$Cl$_2$)/nm (log~$\varepsilon$): 416
(5.44), 530 (4.29); HRMS (ESI+): $m/z$ cald for C$_{46}$H$_{33}$N$_5$Ni
[M $+$ H]$^+$ 714.21622, found 714.21738.

\subsection{Attempted synthesis of fused{\hfill\break}
[5-(Pyridin-2-methyl)-10,20-bis(p-tolyl)-15-{\ubreak}phenylporphyrinato]
nickel(II) ($\mathbf{Ni}$\textbf{-}$\mathbf{7}^{\boldsymbol{+}}$,$\mathbf{PF}_{\mathbf{6}^{\boldsymbol{-}}}$)}
\vspace*{.5pc}

\inlinefig{fx04}
\bigskip

Nickel(II) porphyrin \textbf{Ni-7} (1.0 equiv), 2,6-lutidine (2.0
equiv) and PIFA (1.0 equiv) were dissolved in dry CH$_2$Cl$_2$
(0.05~M). The reaction mixture was then stirred at room temperature for
1~h, monitoring the progress of the reaction by TLC (SiO$_2$,
CH$_2$Cl$_2$). At that time, an additional amount of PIFA (0.2 equiv)
was added. The mixture was stirred for 1.5~h and a further amount of
PIFA was again added (1.0 equiv). After a total of 23~h of reaction,
the solvent was evaporated. MALDI-TOF: $m/z$ cald for
C$_{46}$H$_{32}$N$_5$Ni$^+$ [M-PF$_{6^-}$] 712.2026, found 712.2006
(assigned to the fused compound); 713.0963 (assigned to \textbf{Ni-7})
and 726.1798 ([M-2H$^+$-PF$_{6^-}$+O] assigned to the fused compound
with a carbonyl function on the bridging carbon atom).

\subsection{Attempted synthesis of fused{\hfill\break}
[5-(Pyridin-2-methyl)-10,20-bis(p-tolyl)-15-{\ubreak}phenylporphyrinato]
zinc(II)
($\mathbf{Zn}$\textbf{-}$\mathbf{7}^{\boldsymbol{+}}$,$\mathbf{PF}_{\mathbf{6}^{\boldsymbol{-}}}$)}

\inlinefig{fx05}
\medskip

Zinc(II) porphyrin \textbf{Zn-7} (1.0 equiv), 2,6-lutidine (2.0 equiv)
and PIFA (1.0 equiv) were dissolved in dry CH$_2$Cl$_2$ (0.05~M). The
reaction mixture was then stirred at room temperature for 1~h,
monitoring the progress of the reaction by TLC (SiO$_2$, CH$_2$Cl$_2$).
At that time, an additional amount of PIFA (0.2~equiv) was added. The
mixture was stirred for 1.5~h and a further amount of PIFA was again
added (1.0~equiv). After a total of 23~h of reaction, the solvent was
evaporated.\ MALDI-TOF: $m/z$ cald for C$_{46}$H$_{32}$N$_5$Zn$^+$
\mbox{[M-PF$_{6^-}$]} 718.1944, found 717.0941 (assigned to the fused
compound with the loss of one proton), 718.1008 (assigned to the fused
compound); 719.0998 (assigned to \textbf{Zn-7}) and 732.0977
([M-2H$^+$-PF6$^-$+O] assigned to the fused compound with a carbonyl
function on the bridging carbon\break atom).

\section{Conclusion} \label{sec4}

In summary, a new straightforward route for the synthesis of
\textit{meso}-(pyridin-2-ylmethyl)porphyrins was developed. This
original pathway involves the nucleophilic attack of
(pyridin-2-ylmethyl)lithium reagent on
10-phenyl-5,15-di-p-tolylporphyrin bearing one free \textit{meso}
position. The obtained free base porphyrin was then metalated providing
the zinc(II) and nickel(II) complexes. These products were
characterized by common analytical techniques (NMR, \mbox{UV--vis.,}
mass spectrometry and electrochemistry). Preliminary attempts to
chemically generate the corresponding C--N-fused compounds (new bond
between the nitrogen of the pyridinyl substituent and the
$\upbeta$-pyrrolic position of the porphyrin) by oxidation with PIFA have
been explored. Unfortunately, none of these attempts have lead to the
formation and isolation of the desired fused porphyrins. Although the
analyses performed on the crude mixtures suggest the formation of the
fused porphyrins with formation of a carbonyl on the CH$_2$ bridge, the
isolation of these compounds to confirm their structure was not
\mbox{successful}.

\section*{Declaration of interests}

The authors do not work for, advise, own shares in, or receive funds
from any organization that could benefit from this article, and have
declared no affiliations other than their research organizations.

\section*{Funding}

This work was supported by the Universit\'{e} de Bourgogne,
Universit\'{e} de Bourgogne Franche-Comt\'{e}, CNRS (Centre National de
la Recherche Scientifique), Conseil R\'{e}gional de Bourgogne through
the ``Plan d'Actions R\'{e}gional pour l'Innovation (PARI)'' and the
``Fonds Europ\'{e}en de D\'{e}veloppement R\'{e}gional (FEDER)''
programs). MB and CHD thank the Agence Nationale de la Recherche for
funding (ANR-15-CE28-0018-01).\ CHD acknowledges the Conseil
R\'{e}gional de Bourgogne Franche-Comt\'{e} for a PhD grant (PORFELEC
project) and the French ``Investissement d'Avenir'' program, project
ISITE-BFC (contract ANR-15-IDEX-03) for funding. 

\section*{Acknowledgments}

The authors are
thankful to Sophie Fournier for technical support, to the ``Plateforme
d'Analyse Chimique et de Synth\`{e}se Mol\'{e}culaire de
l'Universit\'{e} de Bourgogne'' (PACSMUB, \url{http://www.wpcm.fr}) for
ESI-HRMS analyses.

\CDRGrant[ANR]{ANR-15-CE28-0018-01}
\CDRGrant[ANR]{ANR-15-IDEX-03}

\back{}

\section*{Supplementary data}

Supporting information for this article is available on the journal's
website under \printDOI\ or from the author.

\CDRsupplementaryTwotypes{supplementary-material}{\cdrattach{crchim-307-suppl.pdf}}

\bibliographystyle{crchim}
\bibliography{crchim20230919}
\refinput{crchim20230919-reference.tex}

\end{document}
